There is an exact sequence of action here. Scientologists don't just willy-nilly get told the OT III data and "accept" it. The Church member has ALREADY DONE OT 2, and received some of the "Clearing Courses" data which is already grooving the member in REALLY well to the idea of IMPLANTS from a long time ago. Additionally, the member has been AUDITING this stuff on OT II, and getting some sort of results.
For instance when I did OT 2, I hit a point where it felt like somebody pulled the mental rug out from under me. I was blowing charge constantly, non-stop, as if a waterfall had been turned on, but was running up and away from me! The "sensation" or "experience" was pretty "intense" (however anybody else wants to excuse or justify or explain it away). I had NEVER experienced ANYTHING like that before. The heavy-duty tremendous experience locks most members into whatever they think brought the experience about (applying the OT data).
And I was one who was VERY agnostic about it. "OK, I will try it and see what happens". Lots happened! Okay, what does one say to that?
So, first when anybody sits down in the OT III courseroom and opens the pack, he or she is already quite well "set up" for it by already agreeing with many similar related ideas. The gradient has got them by the balls! They have been romanced and finessed up to that point, bit by little bit. The whole stage has been set. Plus, each member has a great deal invested by now - time, money, energy, friends, and family. One has a tendency at this point rather to "accept" it than not.
Also, the person then AUDITS the material. Again, for most people, STUFF happens,, and that includes people who take a very "cautious" view about it all at first.
NO Church member is supposed to contact the information until he or she has completed OT 2. So, it is UNUSUAL for any Church member to read about Xenu, BTs and all of that stuff before one starts the OT III course. All of this talk about, "how can Scientologists be so stupid to believe all this science fiction horseshit", is a very over-generalized and incorrect view of what actually happens.
It is NOT UNCOMMON for a Church member (the large majority possibly) to have absolutely NO IDEA about and NO BELIEF at all in Xenu and related subject material. For most, surely below the level of OT III, it means absolutely nothing.
Generally, a person might come to "believe" in the "fact" of Xenu and related data AFTER having audited the material and gotten ressults of some sort. But that is only after doing the course and auditing the OT III materials.
I did OT III many years ago, and honestly, I never thought about it much afterwards. I sure didn't gather with other OT III's and have "Xenu" discussions or "Xenu church services". I knew friends who audited it too, and they didn't think about it much. Them and I NEVER walked around thinking, "oh, I believe in mighty Xenu". Honestly, with the way the Church has it comparmentalized, I suspect that MOST members (above OT III) only think about it AT ALL, when they HAVE TO, when they are in session dealing with these things. Otherwise, they live their lives like anybody else, and give it very little thought. It is a small part of the life of any Scientologist, but the die-hard critic seems to just love to trounce on it because it seems to be such an "easy target".
There are many REAL things wrong with the C of S; over-concentrating on OT III stuff takes attention away from REAL abuses and crimes.
It is a gross misconception to have the idea that Scientology church members "believe" in Xenu in the same way that Christians "believe" in God or Satan. The OT III data is subject material for an aspect of Scientology THERAPY. Most people, when they leave therapy of any sort, FORGET ABOUT THE THERAPY until the next time. The analogy is not unlike how most Scientology members relate to the OT III information.
In truth, and this probably appplies to people OT III and above too, very FEW Scientologists ever "convince her or himself that Hubbard's 3rd rate Science fiction is historic fact". Most probably just don't give a shit.